MIAMI -- Despite initial hopes to have Drew Storen make his season debut in tonight's second-half opener, the Nationals decided the reliever needs a bit more time on a minor-league rehab assignment to build up his arm strength before pitching in the big leagues.

The Nationals originally planned for Storen to make four rehab appearances with Class A Potomac and then come off the disabled list in time for tonight's game against the Marlins. But Storen (who has missed the entire season to date after surgery to remove a bone spur from his elbow) noted some arm fatigue during the latter stages of his two-inning stint last night at Class A Potomac, and club officials want him to make at least one more rehab appearance, perhaps more.

"The consensus from the coaches that watched him was that his arm strength is not quite where it needs to be, and that he gets a couple days off and then another outing," manager Davey Johnson said. "And then hopefully he'll be at that point where he'll be considered a candidate to be recalled."

Johnson said Storen will pitch one inning in relief, likely on Saturday, for Class AA Harrisburg. After that, he'll be re-evaluated, though it appears unlikely he'd make his season debut before the Nationals' next home game, Tuesday against the Mets.

"Our concern is that he's ready and that he doesn't have to extra stress his arm when he gets up here," Johnson said. "So this is ... making sure his arm is ready so he doesn't have any problems once he gets up here."